In the optical pickup, a laser beam is focused on a recording surface of the optical disk, and the laser beam is detected from the recording surface of the optical disk. The optical pickup is formed by a combination of optical elements such as a laser, a mirror, a lens and a photodetector. For an optical axis of the optical element, position accuracy and inclination accuracy which affect aberration of the laser beam are important in the reading and writing operations.
In the optical pickup, an optical pickup case having high stiffness is used to maintain the position accuracy and inclination accuracy of the optical element. The optical element is directly fixed to the optical pickup case with an adhesive, or the optical element is fixed to the optical pickup case with the adhesive while held by a holding member. In fixing the optical element with the adhesive, unlike the fixing with a screw, it is not necessary to provide a space for a screw threaded portion, so that the adhesive is suitable to the fixing of the small components such as the optical element.
However, curing, contraction, and swelling are generated in the adhesive as time advances or by a change in ambient temperature. Therefore, sometimes the position and inclination are displaced in the optical element.
Japanese Patent Application Laid-Open No. 2002-197718 discloses a method of bonding the optical element at horizontally symmetrical positions in order to avoid the problem caused by the adhesive. Therefore, the displacements of the position and inclination can be decreased in the optical element, even if the expansion or contraction is generated in the adhesive.
In the optical pickup, sometimes an aberration correction element is mounted to correct unevenness of a thickness of a protective layer and a large spherical aberration generated by a layer jump of a multi-layered recording disk.
Japanese Patent Application Laid-Open No. 2003-91847 discloses an aberration correction element including a lens moving mechanism which moves a lens. The lens moving mechanism includes a drive motor, a guide shaft, and a lens holding member for holding the lens. Therefore, the aberration correction element is much larger than other optical elements in weight and size. As with other optical elements, it is also necessary that the aberration correction element be mounted in the optical pickup case with high accuracy.
In the optical element in which the drive motor, the guide shaft, the holding member for holding the lens are provided around the lens, like the aberration correction element, it is difficult that the lens is arranged in the center position of the optical component. Therefore, usually the lens is attached while offset from the center position of the optical component.
In such structures, the change in ambient temperature easily causes the displacements of the position and inclination of the lens. When the optical axis is displaced by the displacements of the position or inclination of the lens, the aberration is generated in a spot of the laser beam focused on the recording layer of the optical disk, which results in the problem that high-density recording is hardly performed.